1. Field of Invention
This invention relates to a stencil printing machine, and more particularly to a stencil printing drum in a stencil printing machine.
2. Description of Related Art
A conventional ordinary stencil printing drum comprises: a rotary cylindrical drum having an ink passage part; an ink supplying roller which is provided inside the rotary cylindrical drum in such a manner that it is brought in contact with the inner cylindrical surface of the rotary cylindrical drum; and an ink coating roller for supplying ink to the ink supplying roller. The ink supplying roller is so arranged that it is rotatable around an axis in parallel with the central axis of the rotary cylindrical drum and is brought into contact with the inner cylindrical surface of the rotary cylindrical drum. The ink coating roller is in parallel with the ink supplying roller, thus forming an ink pool between them. That is, the ink coating roller is adapted to coat the surface of the ink supplying roller with ink.
When ink is supplied to the inner cylindrical surface of the rotary cylindrical drum by the ink supplying roller, part of the ink thus supplied may leak out from both ends of the ink supplying roller, and run to the inner cylindrical surface of the rotary cylindrical drum. In order to overcome this difficulty, a spatula-shaped plate member is provided inside the rotary cylindrical drum in such a manner that it is in contact with the inner cylindrical surface of the rotary cylindrical drum. That is, the ink thus run is returned by the spatula-shaped plate member to the ink coating part of the inner cylindrical surface of the rotary cylindrical drum where the ink supplying roller coats the ink.
However, it is rather difficult to determine the contact pressure and the contact angle between the spatula-shaped plate member and the inner cylindrical surface of the rotary cylindrical drum. Hence, it is also difficult for the spatula-shaped plate member to return all of the ink to the ink coating part of the inner cylindrical surface of the rotary cylindrical drum. The ink which is not caught by the spatula-shaped plate member may flow out of the printing drum to stain the printing machine or the printing sheets. In addition, the spatula-shaped plate member is worn out soon being held in contact with the inner cylindrical surface of the rotary cylindrical drum at all times.